1. Field of the Invention
The present invention relates to a light scanning device and a method thereof. More particularly, the present invention relates to a light scanning device and a method thereof capable of standardizing an interface by simplifying control signals inputted to the light scanning device and reducing the size of a connector for signal connection in an apparatus including the light scanning device, such as a printer or multifunction machine, using a laser beam.
2. Description of the Related Art
An electrophotographic image-forming apparatus performs a printing operation in the following way. First, a light scanning device scans light, corresponding to inputted image data, onto the surface of a photosensitive drum uniformly charged to a voltage. An electrostatic latent image is formed on the surface of the photosensitive drum and when toner is supplied on the surface of the photosensitive drum, a toner image is formed on the electrostatic latent image.
A transfer roller then transfers the toner image formed on the photosensitive drum onto a recording paper. Next, the toner image transferred to the recording paper is fixed onto the recording paper by high heat and pressure of a fixer and then discharged from the image-forming apparatus.
FIG. 1 is a block diagram of a light scanning device included in a general image-forming apparatus. The light scanning device includes a light output controller 100 and a light output part 110. The light output controller 100 receives four sample and hold (referred to as S&H hereinafter) signals IN1, IN2, IN3, and IN4 from a controller (not shown). In this case, the controller is acting as a S&H signal generator. Since the light scanning device of FIG. 1 generates four lights, it is called a quad beam scanning device.
The light output part 110, generally called a quad beam semiconductor laser, includes four light-generating parts 120, 122, 124, and 126 generating respective lights and a light-output amount sensor 128. The light-generating parts 120 through 126 are generally realized by laser diodes and the light-output amount sensor 128 is realized by a photodiode. Since the laser diodes have a characteristic in that their light output changes depending on environmental conditions, particularly temperature, a photodiode monitoring the light output is required.
FIG. 2 is a waveform diagram illustrating four S&H signals IN1, IN2, IN3, and IN4 provided to the light scanning device of FIG. 1. Here, a gray-colored region marked by ‘S’ is a sampling interval and the region marked by ‘H’ is a holding interval.
The light output controller 100, generally called an automatic power controller (APC) circuit, controls the light output part 110 to maintain a constant light output. The light output controller 100 is generally realized by a driver integrated circuit (IC).
For sequential sampling intervals of the four S&H signals IN1, IN2, IN3, and IN4 having the waveforms of FIG. 2 inputted from the controller, the light output controller 100 generates light by having an electrical current flow through the respective laser diodes 120, 122, 124, and 126. Next, the light output controller 100 receives a voltage from the photodiode 128 reacting to the generated light. Using the voltage, the light output controller 100 sets a control signal value to be maintained for the holding intervals of the S&H signals IN1, IN2, IN3, and IN4. The control signal value is an electrical current value associated with an amount of electrical current flowing through the laser diodes 120, 122, 124, and 126. That is, it is possible to suppress fluctuations in a light output due to temperature by setting a current that reflects the respective light-output amounts monitored by the photodiode 128. In the case where the light output controller 100 is realized by a driver IC-type APC circuit, a detailed operation thereof will be described below. When the laser diodes 120 through 126 initially emit light, a capacitor (not shown) connected with an external terminal of the APC circuit 100 is charged and discharged according to a difference between a reference voltage and a feedback voltage output from the photodiode 128, so that light output is maintained at a constant intensity. The above operation is performed for the sampling intervals of the S&H signals IN1, IN2, IN3, and IN4. Since the capacitor is in a high impedance state for the holding intervals, the capacitor does not perform a light-output control function for the holding intervals.
Since only one photodiode 128 for the four laser diodes 120 through 126 is provided, times at which the respective laser diodes 120 through 126 generate light are differentiated in order to individually obtain feedback voltages from the photodiode 128 that correspond to light generated by the respective laser diodes 120 through 126. For that purpose, four S&H signals IN1, IN2, IN3, and IN4, such as the waveforms in FIG. 2, are generally provided.
Since the conventional quad beam scanning device requires four S&H signal inputs as described above, it is difficult to set a margin for an input control time. Also, since the related art quad beam scanning device requires a plurality of input signals, it is difficult to standardize an interface and it is difficult to make a small connector for signal connection. As such, a compact apparatus is difficult to realize.
Accordingly, there is a need for an improved light scanning device and a method thereof that allows for an interface to be easily standardized and for a reduced size signal connector.